This invention generally relates to vehicles running on tracks of a roadway and carried by support structures provided with support wheels and with guide wheels located symmetrically with respect to stationary guide means and having tires running on the guide means. It more particularly relates to an apparatus for detecting deflation of one of the guide wheel tires.
The invention is particularly, but not exclusively, suitable for use in guided self-propelled vehicles of a mass transportation system having horizontal rubber wheels carried by the axles and rolling on a pair of guide bars or beams placed symmetrically with respect to a longitudinal midplane of the tracks, or on a single guide bar which they straddle: such vehicles are for example used in the VAL public transportation system at Lille, France.
Deflation of a guide wheel of such a vehicle should be detected without delay since, even if safety guide devices are provided, prolonged traveling on an insufficiently inflated or flat guide wheel tire may result in burst or fire or at least considerable disturbances in operation.
Different devices have already been suggested for providing an alarm signal if a guide wheel tire is deflated or flat. Some use a sensor carried by the wheel and which supplies a signal transmitted inductively to a receiver mounted on the body of the vehicle (French specification No. 1,399,657). The arrangement is complex since it requires a sensor and a transmission system on each tire-equipped wheel. Devices are also known for detecting the deflation of guide wheel tires which detect the deformations or stresses in the guide bars or in their support (French No. 2,323,138). They are complex and of limited reliability; they require an increased flexibility of the guide bars in detection zones, result in costly machining and local weakening of the guide bars.
It is an object of the invention to provide an improved apparatus for detecting the deflated or flat condition of normally inflated guide wheels. It is a more specific object to provide such an apparatus which is of moderate cost and sufficiently reliable.
For that purpose, there is provided an apparatus suitable for use in a mass transportation system comprising a roadway having parallel supporting tracks and stationary guide means parallel to said tracks and vehicles. Each vehicle is provided with a support structure having support wheels rolling on the tracks and guide wheels provided with inflated tires in rolling contact with the guide means of the roadway and symmetrically located with respect to the guide means. The apparatus for detecting deflation of any one of the tires includes sensor means for detecting lateral offset of the support structure with respect to the tracks from a set position and signal delivering means connected to the sensor means to provide a signal when the offset exceeds a predetermined value.
The approach to the problem used by the invention is different from those previously suggested. The apparatus has no movable or flexible element. There is no component of the apparatus on board the vehicles. It is based on the finding that the probability of simultaneous and symmetric deflation of two opposed guide wheels is extremely low.
The sensor means will typically be carried by the roadway and placed so as to detect movement of the support structure with respect to a component thereof, for example with respect to the guide means. To increase the amount of offset of the support structure in the event of deflation of a tire at detection locations, distributed along the tracks and provided with sensors, the guide means are arranged for imposing on the tires an increased transverse load at these locations. If the guide means comprise two parallel bars, load increase may be obtained by a local decrease in the distance between the two bars. If the guide means comprise a single bar which is straddled by the guide tires (as for instance in the transportation system described in British Patent Application No. 2,019,073), the load may be locally increased by thickening the bar. Anyway, if the left and right hand guide wheels are inflated substantially identically, there is no appreciable lateral offset of the support structure and guide wheels when passing across the zone where the bars are closed up or the single bar is of increased thickness. If on the other hand a tire is deflated or flat, the tires have differect stiffnesses and the support structure moves transversely until the horizontal forces applied to the guide wheels are balanced. The amount of offset of the support structure will depend on the amount of closing up or thickening.
This closing up or this thickening is of great advantage because, in the regular portion of the tracks, the amount of offset may be so low that it would not be possible to distinguish that offset from those resulting from normal free movements, particularly in bends, due to different causes (lack of uniformity of the tracks, braking forces, wind action, centrifugal force in a curve). The amount of required offset will be selected for avoiding excessive forces on the guide wheels and their supporting structure during normal operation. In practice, the closing up or thickening will be chosen so that the stresses which it causes do not exceed those met with in the curves of the tracks during normal operation. On the other hand, such closing up or thickening will be selected to cause an appreciable amount of offset, typically of the order of magnitude of one centimeter, should a wheel be flat.
A part of the supporting structure (or on members connected thereto) which is close to the rolling plane is preferably subjected to measurement. If the supporting structure is connected to the vehicle body for free yaw movement, measurement will take place at a point remote from the yaw axis. The sensor means will typically comprise at least one contactless displacement sensor, which may be associated with a circuit which supplies an alarm signal only when the signal supplied by the sensor exceeds a threshold. Since the part whose offset is detected is generally of metal, electromagnetic proximity sensors of a conventional type may be used.
The invention will be better understood from the following description of particular embodiments given by way of examples only.